In prior-art COP (capacitor on plug) devices, contact plugs are often used as vertical interconnects between metal lines in multilevel interconnect schemes During processing of a CW (contact window) hole opening using an oxide reactive ion etch (RIE), oxygen forms in the TEOS (Tetraethyl Orthosilicate) hardmask covering the capacitor. An Ir (Iridium) based barrier is often positioned between a bottom electrode (BE) and the TEOS substrate to block oxygen from causing damage when it diffuses to the plug. However, TEOS residues of the etching process (“fences”) can form during RIE processing of the bottom electrode. These fences allow the oxygen to diffuse from the TEOS hardmask to the plugs during the CW hole RIE processing. This oxygen reacts with the material of the plug, for example poly silicon or W (Tungsten), causing functional damage to the plug structure, in particular causing contact degradation.
One way to avoid this plug oxidization problem is to make the bottom electrode RIE process such that no oxygen-diffusion-allowing fences are formed. However, this is difficult to achieve in typical processes where the hardmask covering the bottom electrode during bottom electrode RIE processing has a steep taper angle.
Another way to avoid this plug oxidization problem is to remove the TEOS fences after they are formed. However, this is a difficult and complex process.
FIG. 1 illustrates the above problem as found in a ferroelectric capacitor device 11 of the prior art. A ferroelectric (FE) capacitor 13 includes a ferroelectric layer 15 sandwiched between a bottom electrode 17 and a top electrode 19. The ferroelectric layer 15 can include PZT, SBT, or BLT, for example. The top electrode 19 is covered with a TEOS hardmask 21 used during patterning of the top electrode. The TEOS hardmask 21 and capacitor 13 are also encapsulated by an Al2O3 oxygen barrier layer 22. The capacitor is covered by an additional TEOS hardmask 23 used during patterning of the bottom electrode 17. This additional TEOS hardmask 23 is encapsulated by an additional Al2O3 barrier layer 24.
A Ti glue-layer 25 serves to adhere the bottom electrode 17 to a TEOS substrate 27 of the FE capacitor 13. A plug 29 (made from poly silicon, for example) passes through the device 11 to form an electrical connection between an active region (not shown) and the bottom electrode 17. Between the Ti glue-layer 25 and the bottom electrode 17 can be barrier layers 31 of Ir (Iridium), IrO2 (Iridium Oxide) or other materials for blocking oxygen diffusion. During the processing of the capacitor 13, oxygen RTA or other high temperature oxygen treatments are used. These barrier layers 31 stop the oxygen introduced from these processes from damaging the plug 29.
Metal fences 33 and TEOS fences 35 can be formed during the RIE processing of the bottom electrode 17. During processing of a CW hole opening 37 using an oxide RIE process, oxygen (schematically illustrated by the dots 39) enters the additional TEOS hardmask 23. As shown schematically by the dots 39, the oxygen travels from the additional TEOS hardmask 23, through the TEOS fence 35 and through the TEOS substrate 27 to the plug 29, causing damage to the plug 29. The oxygen can similarly pass to W-plugs causing damaging oxidation.
It would be desirable to have sidewall structures and sidewall forming processes for reducing the contact plug oxidization.